Recent trends indicate that local area wireless networks based on IEEE 802.11 standards and third-generation wide area wireless networks such as code division multiple access 2000 (CDMA2000) and universal mobile telecommunications system (UMTS) will co-exist to offer Internet access to end users. The two technologies offer characteristics that complement each other. The 802.11 standards allow the realization of economical Wireless LANs that support data rates anywhere from about 1 Mbps to about 54 Mbps based on the distance to the base station (often called Access Points). However, 802.11 Access Points can cover areas of only a few thousand square meters, making them suitable for enterprise networks and public hot-spots such as hotels and airports. On the other hand, wireless networks built using the 3G standards require significant capital investments, support limited peak rates that range from 64 Kbps to nearly 2 Mbps as a maximum, but offer a much wider area of coverage that enables ubiquitous connectivity. The deployment of architectures that allow users to seamlessly switch between these two types of network would present several advantages to both service providers and users. By offering integrated 802.11/3G services, 3G operators and Wireless Internet Service Providers (WISP) could capitalize on their investments, attract a wider user base and ultimately facilitate the ubiquitous introduction of high-speed wireless data. Users would benefit from the enhanced performance and lower overall cost of such a combined service.
The design of a network architecture that efficiently integrates 3G and 802.11 is a challenging task, particularly when an objective is to make the interoperation between the two technologies as seamless and as efficient as possible, both from the end-user's and from the operator's perspectives. Wireless LANs, originally targeted at enterprise and home networks, lack many of the capabilities which are essential in public environments. These capabilities include unified and universally accepted authentication, accounting and billing mechanisms; the integration of mobility mechanisms with QoS and application-level services; the support for heterogeneous network architectures through the implementation of roaming agreements. Conversely, although these characteristics are present by design in 3G networks, their implementation depends on specific wireless access architectures such as CDMA2000 or UMTS and their extension to other wireless technologies such as 802.11 presents several compatibility issues. Depending on the level of inter-dependence that one is willing to introduce between 802.11 and 3G, the design of integrated multi-technology wireless systems can lead to network architectures that have fundamentally different properties.
In 802.11 networks, Access Points (AP) bridge the wireless and wired parts of the network. However, the current 802.11 protocol suite only defines the physical and media access control layers but not the layers above. There are three implications of this. First, authentication procedures vary from provider to provider, depending on the particular architecture and set of authentication protocols that they decide to deploy. Second, existing standards do not define the characteristics of the services offered to users, for example with respect to QoS guarantees. Finally, there is currently no agreed upon mobility-management mechanism that would allow users to seamlessly roam across different 802.11 networks managed by different providers.
In 3G networks, Base Stations (BS) together with Radio Network Controllers (RNC) bridge the wireless and wired network. There are two dominating 3G standard suites —CDMA2000 and UMTS. In the case of CDMS2000, the Packet Control Function (PCF) and Packet Data Service Nodes (PDSN) channel data packets to the Internet through the provider's core network. In the case of UMTS, the Serving and Gateway GPRS Service Nodes (SGSN and GGSN) provide logically similar functionalities. Unlike 802.11, 3G standards cover also the layers above the media access, so protocols that deal with authentication procedures, QoS guarantees, and mobility management are standardized. Users are guaranteed that they can seamlessly roam across 3G networks owned by different providers, assuming that they share a roaming agreement.
Ala-Laurila et al., “Wireless Lan Access Network Architecture for Mobile Operators”. IEEE Communications Magazine, pp 82-89, November 2001, proposed a solution that combines GSM/GPRs subscriber management and billing mechanisms with 802.11 access technology. They assume user terminals (laptops or PDAs) are equipped with GSM SIM readers and use authentication procedures similar to those in GSM/GPRS networks. They use a special protocol called NAAP that runs on top of UDP/IP to transport authentication messages. They do not study the use and implication of dual-interface (GSM/GPRS and 802.11) terminal. Therefore, their system supports roaming but does not support seamless hand-off that preserves on-going sessions between the two networks. If the two networks use two different access technologies, the user has to manually configure the terminal to use a different network interface. Finally, their system does not provide QoS guarantees in 802.11 access network and also, does not optimize web delivery over mobile-IP sessions.
J. H. Park, “Wireless Internet Access for Mobile Subscribers Based on the GRPS/UMTS Network”, IEEE Communications Magazine, pp 38-49, April 2002, studied how ISP subscribers visiting a foreign GPRS/UMTS network can authenticate themselves and use the GPRS/UMTS network. This work focuses on the case where the home network (and the AAA infrastructure) is an ISP network and the access network is a GPRS/UMTS network. Park also studied deployment of mobile-IP in their context.
Weinstein et al., “Wireless Lan and Cellular Mobile—Competition and Cooperation”, IEEE Micro Magazine, to appear, proposed a scenario where 802.11 access networks complement rather than compete with cellular access networks. They noticed the importance of dual-mode radios and coordinated AAA, but they do not address the issue of seamless inter-technology hand-off.
Brustoloni et al., Microisps: Providing Convenient and Low-Cost High-Bandwidth Internet Access”, Computer Networks, 33(1-6): pp 789-802, 2000, proposed an architecture called microISP for hot-spot operators offering service in airports, hotels, etc. In their architecture, an operator leases a high-speed back-haul link to a conventional ISP, and provide high-speed Internet access to transient users using 802.11 access network. In their case, there is no notion of roaming agreement, and the users are expected to settle payment individually for each session.
An improved system for integrating 3G and 802.11 access is desired.